1. Field of the Invention
The invention relates to a convoluted air spring assembly for vehicle suspensions.
2. Background Information
Convoluted air spring assemblies typically include two end plates or bead plates sealingly connected to respective ends of a hollow fabric reinforced rubber bladder. These air springs are used primarily for implementation in motor vehicles for supporting the vehicle body or for use in other types of equipment subject to shock to provide cushioning therefor. The air springs are sealed at the ends to form a pressurized fluid chamber within the bladder. An air spring will generate a certain load at a given height and pressure. Upon the air spring experiencing a road displacement input, the bladder will begin to collapse or extend as the end members move toward or away from each other, respectively, to yield predictable dynamic load characteristics.
These dynamic load characteristics of the air spring are a function of the internal air pressure, volume and effective area. For a given height, the effective area is determined by dividing the air spring load by the internal pressure. The effective area of a convoluted air spring is typically only controlled by the maximum inflated diameter and length of the fabric reinforced rubber bladder. The effective area varies with the air spring height.
Often it is desirable to tailor the dynamic load characteristics of the convoluted air spring, such as dynamic spring rate and natural frequency, to fit a particular vehicle or application. Typically, this is accomplished by adjusting the internal volume or fluid type within the flexible bladder. When these parameters are established, it is necessary to modify the effective area.
Heretofore, once the bladder is inflated to its maximum air pressure, a larger bladder is required to provide for increased load capabilities of the air spring. However, it is not always practical to change the bladder size for all applications. For example, some vehicles have certain space limitations, which do not allow for a larger bladder size. Additionally, changing the bladder size may affect other characteristics of the air spring.
U.S. Pat. No. 6,345,813 shows an air spring having a pair of support rings with outer surfaces over which the sleeve moves as the air spring changes height to effect the spring rate. Although such a structure may by satisfactory for many applications, it may not be suitable in certain applications where there is articulation or the available height is at a minimum due to the trapping and pinching of the expanded sleeve between the outer surfaces of the pair of opposed support rings.
What the art needs is an air spring assembly, which allows for control of its effective area in order to achieve certain dynamic load characteristics without having to significantly change the physical size of the bladder.
The invention changes the effective area of the convoluted air spring by using a skirt on each bead plate that controls the shape of the bladder as the air spring travels between its maximum extended height and its minimum collapsed height. It is the change in effective area with respect to the air spring height that changes the dynamic load, thus effecting the dynamic spring rate.
Adding such skirts to both ends of an air spring may cause clearance issues at the fully collapsed height, especially if both skirts protrude toward each other. This invention uses a skirt, typically, but not restricted to, mounting on the upper bead plate that protrudes or tapers down toward the other bead plate. The other skirt, typically, but not restricted to, mounting on the lower bead plate tapers away from the opposite skirts. Such skirts are then complementary having one skirt which forces the inflated bladder over the other skirt until they are nestling close together at the fully collapsed height. This, in essence, translates vertical clearance into horizontal clearance while still substantially persuading the effective area.